This invention relates to valves for controlling the flow of fluid and more particularly to a valve in which a closure member rotates between opened and closed positions in which the sealing member between the valve body and closure member engage only upon the application of exterior pressure unrelated to the pressure within the valve.
Valves having a spherically shaped closure member rotating between open and closed positions within the body of the valve are usually referred to as ball valves. The rotating closure, however, has little structural relationship to a ball, the only similarity being the spherical maximum surface of the closing member. It is sometimes referred to as a ball herein. Seats in the body engage this maximum spherical surface at two opposing surfaces when the valve is closed and at two opposing surfaces 90 degrees from the first said surfaces when the valve is open. A flow passage continues through the ball within the seat diameters when the valve is in the open position. In the closed position, the closure member usually is solid within the seat diameters.
Historically, floating ball valves have had one or more seats which constantly engage the outer surface of the ball. When the ball is in the closed position in a xe2x80x9cfloating ballxe2x80x9d design, upstream forces force the ball against the downstream seat. The force on this seat is equal to the upstream pressure minus the downstream pressure times the area enclosed by the sealing surface.
In some ball valve designs, called xe2x80x9ctrunnion ballxe2x80x9d valves, the ball is fixed in lateral position by two trunnions or bearings at the top and bottom of the ball. In this case, the upstream seat is activated by pressure and the maximum force acting against the ball is equal to the area between the outside of the seat and the sealing diameter of the seat. It can be seen that low pressure valves favor the floating ball design where the seat force is equal to the entire area inside the sealing diameter. However, high pressure valves favor the trunnion valve design where the seat force is limited to the area between the outer and inner diameters of the upstream seat. The torque necessary to turn a valve having trunnions is much less than that of the floating ball valve design because the radius of the bearings is quite small. On the floating ball valve design the turning torque is resisted by the seat surfaces acting on the exterior of the ball.
With the seats constantly engaged, some problems are encountered with both trunnion and floating style balls. The seats themselves are usually lower modulus materials or have a small enough cross section to have an effective lower modulus. These seats can be abraded as the ball surface rotates against them. Secondly, as the ball just begins to open, high pressure forces tear at the seat. This action is called wire drawing. Surface adhesions, grit sand and other foreign materials in the liquid can also abrade away the seat or get under the seat and prevent it from sealing properly.
Some valves also have to operate with pressure extremes ranging from very low pressures to very high pressures. The floating ball valve design favors low pressure operations because the area exposed to line pressure is much greater. However, if a large floating ball valve is exposed to very high pressures, the force necessary to turn the valve can be extremely burdensome and can tear away the seat material. On the other hand, a trunnion style valve operating at very low pressures can have insufficient seat force to create a seal under some conditions. To overcome this, trunnion valves usually have seat springs urging the seat against the ball which create a minimum force necessary to obtain the sealing relationship with the ball under most normal conditions even at very low or zero pressures.
In my new design, the seat force is totally independent of line pressure. The valve can be of either the trunnion style or a floating ball, but the pressure against the upstream seat is controlled by external pressurexe2x80x94the force on the seat can therefore be very high when desired to affect a tight seal but can be zero when it is desired to rotate the ball.
The seat springs are also reversed. Instead of forcing the seats against the sealing surface of the ball with a minimum selected force, the seat springs work in the opposite direction to retract the seat to maintain a minimum clearance when the ball is being rotated.
In a trunnion design the upstream seat force against the ball is reacted by the trunnions. In a floating ball design the upstream seat force is reacted to by the downstream seat. In either case, the seat is only actuated when the ball is in the static position, either opened or closed. In a floating ball design, it may be desirable to have a fixed seal on the downstream side so that xe2x80x9cdouble block and bleed,xe2x80x9d that is, simultaneous upstream and downstream sealing, can be obtained. In a trunnion design it may be necessary in some cases to have both upstream and downstream seats activated separately by exterior forces.
In the proposed design, flush ports are provided at both sides of the valve. When the seats are engaged with the valve in the closed position, flush ports can be used to pass clean fluids through the valve, removing any material which may have caked up in the bore of the valve or around the sealing surfaces. With seats engaged and the valve in the open position, the flush ports can be used to clean the closure surface of the ball. The flush ports can also be used to measure the pressure within the valve body when the seats are in the actuated position. If this pressure is zero it is an indication the valve is sealing tightly and there is no leakage whatsoever around either upstream or downstream seat. Such a feature is offered in certain valves and is known as double block and bleed. By this it is meant that both upstream and downstream seats are sealing against external pressure. The interior of the valve can be bled to zero and the lack of any flow indicates that both seats are working.
Another improvement in this design lies within the sealing member itself. The seat, in effect, is an annular piston actuated by external pressure. The seal mechanism which engages the surface of the ball is a small rectangular cross section metal ring which juts out slightly ahead of the surface of the seat to engage the ball in a sealing relationship. The metal ring is constrained laterally but allowed to expand or deform vertically to make up for minor inconsistencies of the ball and to assure a good sealing surface. Around the seat between the sealing member and the seat itself is injected a low modulus elastomer material which serves to keep out any foreign material, but is not stiff enough to keep the seat from radially expanding. The modulus of elasticity of injected material is less than 1 million pounds per square inch per inch whereas the seat material is at least 14 million pounds per square inch per inch and usually as high as 29 million pounds per square inch per inch.
Another improvement incorporated into this valve is in the stem design. Two bearings are provided for the stem; one near the lower end and one near the upper end. Both bearings are made from exceptionally hard material and each has grooves cut therein to serve as a receptacle for any grit that might get into the stem area. The stem itself is hardened in the area where the bearings contact so that you have two hardened surfaces bearing against each other. The upper stem bearing serves to prevent any off center movement of the stem due to actuator or handle inputs. The lower stem bearing prevents any off center movement of the stem bearing due to high forces arising from the ball sticking.
The stem also has a dirt excluder seal at its lower end. This prevents grit and line debris from entering up the stem cavity and getting in the bearings. At its upper end, the stem is retained in position by a snap ring. This is to make sure that no one can over tighten or under tighten the stem nut normally provided. The snap ring is in a precise location to allow the stem slight clearance so that it rotates in the bearings freely.
Other features and advantages of the invention will be apparent from the following specification and drawings.